As Thomaskantor Bach performed a cantata every Sunday in the Leipzig churches. He composed most of the pieces himself, being supported in the production and in the rehearsals by experienced Thomas musicians. The examination of the manuscripts of the Thomaner helps us today to date the origin of Bach's works more precisely. Many of the original performance voices remained in the Thomasschule after Bach's death. In 1951 they were transferred to the Bach Archive for permanent storage.